Dihedral bladed ventilating fan



Dec. 17, 1968 H. R. BOHANON 3,416,725

DIHEDRAL BLADED VENTILATING FAN Filed Oct. 12, 1967 2 Sheets-Sheet 1 F/G 2 mvmon HOY R. BOHANON RNEQ,

Dec. 17, 1968 o o 3,416,725

DIHEDRAL BLADED VENTILATING FAN Filed OO'C. 12, 1967 2 Sheets-Sheet 2 5/4415 was INVENTOR 14 0) I?- 50%4000 BY Semmes & sehzmes ATTORNEY United States Patent 3,416,725 DIHEDRAL BLADED VENTILATING FAN Hoy R. Bohanon, Muskogee, 0kla., assignor to Acme Engineering and Manufacturing Corporation, Muskogee, 0kla., a corporation of Oklahoma Filed Oct. 12, 1967, Ser. No. 674,814

8 Claims. (Cl. 230-259) ABSTRACT OF THE DISCLOSURE Dihedral angle on blade with respect to plane of rotation such that net lift force on blade has radial component to help turn air as well as axial component providing increase in total pressure as air passes through fan.

BACKGROUND OF THE INVENTION In a propeller type exhaust fan mounted within an essentially fiat wall, air converges toward the fan from all directions and discharges through the opening in the wall. The air flow is generally perpendicular to the surfaces of hemispheres centered on the fan opening a short distance from the inlet. In designing wall fans of this type, one of the main problems is to produce a flow pattern that will fill the fan opening. This requires turning the air which moves along the wall almost 90 to thus move in a direction generally parallel with the axis of the fan.

The classical solution to this problem is to employ a large nozzle inlet to turn the air ahead of the fan blades thus establishing a uniform rectilinear air flow pattern through the blades. Technically, such a theoretical solution would provide high efiiciency. However, the nozzle inlet would have to have a large diameter, approximately 50% larger than the fan diameter, which is not economically feasible for commercial fans. That is, the inlets of commercial fans are not large enough to produce this uniform rectilinear flow pattern.

The large nozzle inlet produces a reduced pressure on its curved surface creating a radial component of force that turns the air from a radial to an axial direction. If the nozzle is too small, it does not have enough :area to produce enough force and thus loses control of the flow. In this case, the necessary auxiliary radial forces can be created on the fan blade to cooperate with the limited radial forces available on the small nozzle to produce the desirable flow pattern needed for efiicient fan operation.

SUMMARY OF THE INVENTION These auxiliary radial forces are developed by providing each blade with a dihedral angle in relationship to the plane of rotation such that the net lift force on each blade has a radial component helping to turn the air as well as an axial component providing the increase in total pressure as the air goes through the fan. The ratio of the radial and axial components is equal to the tangent of the dihedral angle which varies along the blade length, being the greatest near the tip of the blade.

The present design is particularly helpful for fans with high flow coefiicients, i.e. fans with a large ratio of air through velocity to blade speed. In such fans having high flow coefficients, the losses due to poor flow patterns are of largest magnitude in spite of the fact that these high flow coefficient fans are most desirable for ventilating purposes since they are smaller and more economical for a given flow capacity, or can operate at a lower speed.

DESCRIPTION OF DRAWINGS FIG. 1 is a top view partly in section illustrating the principles of the present invention, particularly the desirable flow paths and force vectors needed to produce these paths;

. 3,416,725 Patented Dec. 17, 1968 FIG. 2 is a top view illustrating the several blades of the fan assembly, particularly the blade angle distribution and the dihedral angles of the individual Iblades;

FIG. 3 is a view taloen along line 33 of FIG. 2;

FIG. 4 is a view taken along line 44 of FIG. 2;

FIG. 5 is a view taken along line 5-5 of FIG. 6;

FIG. 6 is a perspective view of an embodiment of the present invention illustrating six blades;

FIG. 7 is a schematic diagram illustrating definitions of wing theory applicable to the present invention; and

FIG. 8 is a schematic view taken along line 8-8 of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT To provide a proper foundation for describing the three-dimensional construction of the fan blade of the present invention, the following definitions are presented in relationship to FIGS. 7-8 of the drawings:

The camber line on a blade is the line midway between the suction and pressure surfaces of the blade and parallel to the direction of the motion. This line is generally curved and determines many of the aerodynamic qualities of the blade.

The blade axis is the line between the leading edge and the trailing edge of the blade. Mechanically it is halfway between the two, but aerodynamically it is one quarter of the way from the leading edge to the trailing edge.

The wind vector V is the average velocity direction and magnitude as the air goes through the blade, at the radius under consideration.

The lift vector L is perpendicular to the wind vector and the blade axis, and this is used to provide the lift direction needed.

The dihedral angle is the bend in the blade axis in a plane perpendicular to the blade chord.

Finally, it is to be understood that the lift force on the air is equal and opposite the lift force on the blade.

The principles of the present invention are illustrated in FIG. 1 wherein the reference numeral 10 designates the desired flow paths passing through a wall fan designated generally by the reference numeral 12. The design of blades 14 constitutes the heart of the present invention. Within wall 16 is mounted nozzle 18.

Each of the blades 14 is cambered and twisted such that the blade angle on the inlet edge is less than the blade angle on the outlet edge at a given radius and the average blade angle increases progressively from the tip to the roof of the blade. The reference numeral 21 generally designates the blade axis.

The relationship of the dihedral angle theta (0), illustrated in FIG. 1, with respect to the plane of rotation is such that the net lift force on each blade has a radial component R to help turn the air as well as an axial component A that provides the increase in total pressure as the air goes through the fan. The resultant blade lift force on the air L is also shown in FIG. 1. The ratio of the axial component A to the radial component R is equal to the tangent of the dihedral angle theta.

As seen in FIG. 5, the camber line 20 is a circular are, but other configurations can be used. However, the curvature of camber line 20 is opposite the curvature of the dihedral angle theta (0), i.e. the camber curvature is convex to the inlet side while the dihedral curvature is convex toward the discharge side.

With respect to nozzle 18, the radial component of nozzle force is designated by letter r while the axial component of force by letter a and the resultant nozzle force on air by letter n as seen in FIG. 1.

Performance tests have proved the importance of the present design, total efficiencies of over 70% having been achieved. lmportantly, tests show that increasing the size of the nozzle 18 does not improve the performance of the fan unit, as is the case with conventionally designed blades. The blades 14 of the present invention allow the use of small nozzles 18 with good efficiencies.

I claim:

1. A fan assembly, comprising a flat Wall having an opening therein together with a fan mounted generally within the opening and having blades defining a plane of rotation generally parallel to the wall, each of the blades having a dihedral angle with respect to the plane of rotation such that the net lift force of each blade on the air has a radial component to help turn the air into the inlet of the fan as well as an axial component providing the increase in total pressure as the air goes through the fan, the ratio of the axial to radial components being equal to the tangent of the dihedral angle.

2. A fan assembly as in claim 1, wherein the dihedral angle varies along each blade being greatest near its tip.

3. A fan assembly as in claim 2, wherein the camber line of each blade is formed as a circular arc.

4. A fan assembly as in claim 3, wherein the curvature of the camber line of each blade is opposite the curvature of the dihedral angle of each blade.

5. A fan assembly as in claim 4, wherein the camber curvature of each blade is convex to the inlet side of the blade and the dihedral curvature is convex towards the discharge side of the blade.

6. A fan assembly as in claim 1, including a nozzle surrounding the opening within the wall.

7. A fan assembly as in claim 6, wherein the nozzle includes a surface terminating at one end in a portion generally parallel to the plane of rotation and at the other end in a portion generally perpendicular to the plane of rotation such that a radial component of force is produced that turns the air being delivered to the fan from a radial direction along the flat wall to an axial direction through the fan so as to supplement the radial component of force produced by the blades.

8. A fan assembly, comprising a wall provided with an opening therein, a fan together with means mounting same within said opening, said fan having blades rotating generally parallel with respect to said wall, each of said blades being provided with means defining a dihedral angle over a substantial part thereof, the resulting dihedral curvature in the area of the leading edge of each of said blades providing a radial component of lift force helping turn the air into the inlet of said fan, said dihedral angle also producing an axial component of lift force Providing the increase in total pressure as the air goes through said fan, the ratio of the axial to radial components being equal to the tangent of the dihedral angle.

References Cited UNITED STATES PATENTS 2,027,647 1/1936 Montgomery 230-120 2,703,556 3/1955 Doty et al 230120 2,895,667 7/1959 Stalker 230120 3,334,807 8/1967 McMahan 230120 ROBERT M. WALKER, Primary Examiner. 

